PCR is a commonly used method to make multiple copies of a DNA sequence for various applications such as DNA cloning for sequencing, diagnosing disease, identifying individuals from DNA samples, and performing functional analyses of genes. In PCR, replication of the DNA sequence takes place in multiple thermal cycles, with each cycle typically having three main steps: denaturation, annealing and extension. In the denaturation step, a double-stranded DNA template is heated to about 94-98° C. for 20-30 seconds to yield single-stranded DNA. In the annealing step, primers are annealed to the single-stranded DNA by lowering the temperature to about 50-65° C. for 20-40 seconds. In the extension step, using a DNA polymerase (such as Taq), a new double-stranded DNA is synthesized by extending the primer that has been annealed to the single-stranded DNA at an optimum activity temperature of the DNA polymerase (75-80° C. for Taq). Appreciably, replication of the DNA is exponential as the new double-stranded DNA formed in a cycle undergoes denaturation, annealing and extension in the next cycle, such that each cycle effectively doubles the number of DNA sequences obtained. In addition to the three main steps mentioned above, an initialization step may be required if the DNA polymerase used is heat activated, and the final extension step of the last cycle may be held for a longer period of time (e.g. 5-15 minutes) to ensure that there are no remaining single-stranded DNA fragments.
Thus, any device for performing the PCR needs to be able to perform the repeated thermal cycles in order for the steps of denaturation, annealing and extension to take place. This involves heating and cooling the reaction to the required temperatures and holding the required temperatures for the necessary lengths of time. Given that temperatures go up to nearly 100° C., existing microfluidic or lab-on-chip PCR devices typically require an external thermal cycler to supply the necessary heat, thereby limiting their true portability and size during use.
Conventional PCR thermal cyclers are typically configured to heat DNA samples contained in polypropylene PCR tubes that have a cylindrical body with a top opening and a taped bottom. The PCR tubes fit into holes provided in the PCR thermal cyclers and are subjected to the heat cycles provided by the PCR thermal cyclers in order to multiply the DNA sample contained in the PCR tubes. Subsequently, the multiplied DNA are removed from the PCR tubes in order for tests to be performed on the multiplied DNA. Thus, it will be appreciated that tests involving the use of DNA currently involve multiple stages. These stages include at least sample collection and storage, placing the sample in PCR tubes, placing the PCR tubes into PCR thermal cyclers and performing the PCR, removing the multiplied DNA from the PCR tubes and performing tests using the multiplied DNA. It is therefore desirable to reduce the number of steps needed for performing tests using DNA in order to minimize errors arising from human handling of the samples at various stages of the process.